Boiler feed water marine and like installations



Nov. 8, 1955 G. ARROWSM1TH BOILER FEED WATER MARINE AND LIKE INSTALLATIONS 2 Sheets-Sheet 1 Filed Nov. 28, 1949 Nov. 8, 1955 s. ARROWSMITH BOILER FEED WATER MARINE AND LIKE INSTALLATIONS Filed NOV. 28, 1949 2 Sheets-Sheet 2 Uitcd tates Patent 1 2,722,920 Patented Nov. 8, 19 55 BOILER FEED WATER MARINE AND LIKE INSTALLATIONS George Arrowsmith, Bolton, England, assignor to Hick, Hargreaves & Company, Limited, Bolton, England Application November 28, 1949, Serial No. 129,734

Claims priority, application Great Britain December 8, 1948 9 Claims. (Cl. 122-451) This invention relates to boiler feed water systems, more particularly of the closed feed circuit type for marine and like installations, and is concerned with developments of the recirculating system of deaeration employed according to British Patents Nos. 531,062, 550,998, 551,063 and 561,366 wherein arrangements are described which provide for a recirculation connection between the discharge of the deaterator and the inlet thereto.

With the increasing use of high pressure superheated steam in boilers, the amount of deaeration normally achieved in the main condenser and accepted as satisfactory for lower pressure boilers, no longer provides the degree of deaeration of the boiler feed water required for present day high pressure steam practice, and the prime aim of the present invention is to provide an improved marine boiler feed system whereby this problem is solved and the desired degree of deaeration of the feed water for high pressure boilers is amply achieved in a simple manner without interfering with the operation of the installation according to the normal well tried closed feed circuit principles.

Another aim of the invention is to aiford facilities enabling the deaerated supply of feed water to be employed or continued under very light loads, such as harbour conditions, and further, in circumstances when the deaeration plant fails, or is put out of commission or closed down for any reason, enabling automatic reversion to the normal closed feed circuit operational practice without the necessity of any elaborate change over of valves.

A further object of the invention lies in the provision of a suitable and convenient source of saturated or low pressure steam available for use in the ships evaporators, distillers or similar equipment.

The invention consists in the installation, in a marine or other closed boiler feed circuit, of a deaerator in a loop or shunt circuit of a boiler feed water supply line such that feed water can be drawn from said line into the deaerator and discharged therefrom back to said line and the deaerator discharge being in hydraulic communication with its inlet, excess feed water discharged from the deaerator over and above that required by boiler demand is recirculated to the deaerator.

The invention further consists in an installation having the features set forth in the preceding paragraph, wherein the deaerator is supplied from a suitable source with heating steam under automatic control which may be such that the deaerator is maintained at approximately constant temperature conditions at all loads on the main feed circuit.

A further feature of the invention resides in the automatic control of the feed water inlet to the deaerator dependent on the level of deaerated water therein and such that flooding is prevented in the event of the deaerator discharge pump failing, the automatic control being also dependent upon the pressure in the main feed circuit so that the inlet is closed in the event of an undue fall of pres sure in the said circuit.

It is preferred to employ a deaerator of the direct contact type, although the prime features of the invention may be carried out by aid of a spray deaerator such as described in British Patent No. 550,998.

The invention also comprises the employment of a deaerator of the direct contact type as a source of supply of saturated steam for use in evaporators, distillers or similar equipment.

Further features of the invention will hereinafter appear.

In the accompanying drawings,

Figure 1 is a diagram of a closed boiler feed circuit for marine purposes constructed and arranged in accordance with the invention;

Figure 2 is a diagrammatic plan view of a drip tray type deaerator showing the ararngement of the spray nozzle sections;

Figure 3 is a diagram of a part of a modified form of boiler feed circuit showing the connections of a deaerator of the spray type.

The invention will be exemplified in its application to one of the typical marine closed feed circuits which are well known, the general or fundamental outline of which will be given below.

Referring to Figure 1, the extraction pump 1 of the main condenser 2, which receives the exhaust from the steam turbine or other steam power unit 3, discharges condensate through a pipe line section, which is identified as A, of the boiler feed water line to the condenser 4 of the steam operated ejector, whence it passes by a pipe line section B to the boiler feed pump 5. From the latter pump the water is carried to the steam boilers 6 by way of a pipe line section C. On the sections B and C, feed heaters may be installed which are fed with steam bled from the turbine, ships auxiliaries or other sources.

The condensate drawn from the main condenser 2 by the extraction pump 1 is comparatively free from dissolved oxygen due to the deaerating eifect of the condenser. It is essential, however, that the system shall be flexible and that feed water can be admitted to or drawn from the system to compensate for the fluctuation in demand and supply between the boiler and the condenser. This is normally accommodated by an additional storage feed tank and a so-called closed feed valve 7 actuated by a float 8 dependent for its operation on the level of the condensate in the sump of the condenser 2. This valve controls the flow of water from the storage tank 9, admitting water therefrom to the condenser when the level of condensate falls under excessive boiler demand and by-passing water to the tank from the pipe line A when the condensate level rises on falling boiler demand.

In carrying the invention into eifect as applied by way of example to a system such as above described, to ac-' complish the desired higher degree of deaeration of the feed water, a deaerator 10 of the drip tray type such as described in British Patent No. 551,063, is located in shunt circuit on the pipe section B. An inlet branch 11 from the said pipe section is connected through a sluice valve 12 and an automatic valve 13 (to be described hereinafter) to one end of a coil or other heat exchange element of a condenser or cooler'14. The other end of said coil or heat exchange element is connected by a pipe 15 to the spray jet pipe or pipes of the deaerator 10. The condenser or cooler 14 is vented to atmoshpere by a pipe 17 and is connected by a pipe 18 to the lower part of the deaerator 10. Air removed from the deaerator is thus passed through the condenser or cooler 14. The emergency automatic valve 13 is of a known type dependent for its actuation both on the pressure in the pipe line B and on the level of the deaerated water in the lower part of the deaerator. The control connections for this automatic valve are shown by broken lines, that for the line pressure being indicated at 19 and that for the water level at 20.

Deaerated water is withdrawn from the deaerator by a pump 21 which delivers through a branch connect on 22 Controlled by a discharge valve 23, to a point 24 on the pipe section B which is nearer to the boiler pumps 5 than the inlet branch 11. Thus the deaerator inlet and discharge are bothon the line section B and are in free hydraulic communication through the intervening length of the pipe line section, so that water taken from this section of the feed line at one point for deaeration passes back to the same line at another point. A feed heater may be included at 25 and a further heater is shown at 26.

Heating steam for the deaerator 10 enters above the spray jets 16, and the pipe 2'7 supplying the steam, from any suitableauxiliary source for example, is supplied through an automatic emergency valve 28 of known kind operated according to the pressure in the feed line section B at a point 29 for example, adjacent the ejector condenser 4. The control connection for the valve 28 is shown at 30 in broken lines.

With the sluice valve 12 and the discharge valve 23 of the deaerator 10 closed, the system may be started up in the normal manner and operated as a closed feed circuit as usual without the use of the deaerator, and the pressure in the feed line sections A and B will be that imposed by the characteristics of the condenser extraction pump 1. On opening the sluice valve 12 and the deaerator pump discharge valve 23, feed water will be admitted to the deaerator spray nozzles (assuming conditions are such that the automatic inlet valve 13 is also open) and the quantity of water passed by these spray nozzles will have no relationship to the condensate load in the main condenser but will be determined entirely by the design of the said spray nozzles and the pressure imposed by the condenser extraction pump 1.

The capacity of the deaerator nozzles is so adjusted as to exceed, by a small margin, the maximum flow quantity required between the condenser extraction pump 1 and the boiler feed pump 5, or some other margin limit. The capacity of the deaerator discharge pump 21 is such as to be easily capable of extracting the whole of the water as admitted through the spray nozzles and delivering such water back in the feed line section B at the point 24 of the delivery branch connection thereto.

According to this arrangement, by bringing in the deaerator shunt circuit, the deaerator will at such times discharge sufiicient deaerated water into the feed section B to meet the demands of the boiler feed pump or pumps 5. When full load quantity is not demanded by the boilers, an excess of deaerated water will be discharged into the system, but this will merely recirculate back (from the delivery connection 24) along the feed line section B to the inlet branch 11 to the deaerator and will again flow through the deaerator. This local or shunt circulation will persist as long as the excess condition in question exists.

The deaerator is safeguarded by the automatic inlet valve 13, as should the deaerator discharge pump 21 be shut down or fail, the water level in the deaerator would rise, thus operating a pilot float valve 31 associated with the lower part of the deaerator and on which the automatic valve 13 is dependent through the control connection 20. The rising of the fioat 32 shuts the automatic inlet valve 13 and any further feed water is thus prevented from entering the deaerator. Further, in the event of failure or the closing down of the condenser extraction pump 1 and consequent fall in pressure in the feed line sections A and B, the automatic inlet valve 13 to the deaerator from the feed line B will shut upon such pressure drop, as will also the other automatic valve 28 (dependent on pressure) in the steam supply pipe 27 to the deaerator and prevent steam entering the deaerator and passing into the boiler feed water line so that both inlet feed water and steam are shut ofi under these conditions.

From the foregoing it will be observed that the deaerator being in a shunt circuit, is not an only link between the condenser and boiler feed pumps. Consequently, should it be necessary at any time to put the deaerator out of commission or should it fail due to any unforeseen circumstance, the normal closed feed system would continue automatically to operate, by-passing the deaerator shunt circuit, without the necessity of any elaborate change-over valves. For the same reason it is not necessary to duplicate the deaerator extraction pump.

A deaerator of the type indicated may be of the lightest possible construction, since it can be entirely free from any stored capacity of deaerated water. Moreover, being in a shunt circuit where weight saving is of the utmost importance, it is not essential to the running of the main closed feed circuit to have a standby pump with its driving motor or turbine.

As the deaerator has its own steam supply, it can be adapted for use independently of operation of the main power plant by providing for the required water pressure in the feed section B. Thus the arrangement can conveniently be made available for harbour or like conditions by installing a harbour pump 33 and connecting its suction to a pipe line 34 connecting with the additional storage feed tank 9 and its discharge to a pipe 35 connecting with feed section B, thus maintaining pressure in this section and enabling the deaerator to function throughout harbour periods. Under such conditions the load of the boilers will be comparatively light and the amount of water circulating through the deaerator may be reduced. One convenient mode of effecting this reduction is to arrange for the deaerator inlet from the vent condenser or cooler 14 to serve two or more spray sections each having a suitable number of nozzles. Such an arrangement is shown in Figure 2 where the deaerator 10 is provided with three spray nozzle sections 36 each of which is fed through an inlet valve 37 from the inlet connecting pipe 15. The spray sections may thus be employed selectively. For example, when in harbour one or two of the spray nozzle sections may be closed down whereby water circulating through the deaerator may be appropriately reduced and with such the power required to drive the deaerator discharge pump 21 is correspondingly reduced.

The use of highly superheated steam for marine propulsion has led to deficiencies in a convenient source of low pressure steam for the ships sea water evaporators and distillers. The deaerator arrangement according to the invention remedies this defect as the deaerator as described above may be made to serve as an ideal source of saturated steam. For this purpose a steam branch 38 controlled by a valve 39 is taken from the deaerator chamber at a point below the drip trays. This branch may be employed for the supply of low pressure steam for evaporators, distillers, and other equipment requiring low pressure saturated steam. Any demand supplied through this branch is made up by additional high temperature steam entering through the deaerator steam inlet 27, and this steam is fully saturated in its passage through the deaerator.

In the foregoing, a direct contact or drip tray type of deaerator has been referred to and illustrated, since in most marine installations this type is generally the most suitable. However, any suitable type of deaerator may be employed, and in a modified arrangement according to the invention as illustrated in Figure 3, a spray deaerator 40 such as is described in British patent specification No. 550,998 may be employed and embodied in the shut circuit described in the above example. Such a spray deaerator may be supplied with heated feed water by having its spray inlet 41 controlled by a valve 42 connected to the feed line B on the outlet side of the feed heater 43 in this section. The discharge pump 21 for the deaerator has its delivery connected to the said feed section through a control valve 23 and at a point 24 nearer the boiler feed pumps than the connection for the deaerator inlet, and as with the drip type deaerator described in the previous example, the discharge 24 and inlet 41 are in hydraulic communication such that when the boiler feed pump demand falls, the excess discharged from the deaerator is recirculated back to its inlet. An outlet or vent 45 for the air extracted in the deaerator chamber is provided at the upper end thereof and according to the temperature of the inlet water a vacuum or slight pressure is maintained in the chamber by connecting said outlet or vent 45 to the main condenser, or to an ejector or to atmosphere in the event of the deaerator pressure being above atmosphere. It is to be understood that the arrangement is otherwise as shown and described in connection with the previous example.

Other types of deaerator, such as the heater type comprising tubes through which the heating steam is passed, may also be employed.

I claim:

1. In a closed circuit boiler feed water system having a condensate extraction pump and a boiler feed pump, the combination comprising a feed water supply line section affording a direct conduit between the extraction pump and the feed pump and having no air admitting communication with atmosphere, a deaerator, a feed water inlet conduit to the deaerator having a junction with said feed water supply line section, a deaerated water discharge conduit from the deaerator having a junction with said feed water supply line section, said last named junction being located between said first named junction of the deaerator feed water inlet conduit and the boiler feed pump, and a pump in said deaerated water discharge conduit for withdrawing deaerated water from the deaerator, whereby feed water is admitted from the said feed water supply line section to the deaerator and discharged back to said line section, and excess feed water discharged from the deaerator over and above that required by boiler demand is recirculated to the deaerator through said feed line section between the aforesaid junctions.

2. A boiler feed water system according to claim 1,

comprising means for supplying heating steam to the deaerator, an automatic emergency valve in said supply means, and means dependent upon the pressure at a convenient point in the feed water supply line section to close the said emergency valve when the feed line pressure falls below a predetermined value, the said emergency valve being normally open.

3. A boiler feed water system according to claim 1, comprising a normally open automatic emergency valve in the water inlet conduit to the deaerator from the feed water supply line section, and means dependent upon the level of the d'eaerated water in the deaerator for closing said emergency valve when such level exceeds a predetermined upper limit whereby flooding of the deaerator in the event of failure of the deaerator discharge pump is prevented.

4. A boiler feed water system according to claim 1, comprising a normally open automatic emergency valve in the feed water inlet conduit to the deaerator from the feed supply line section, and means dependent on the pressure in said supply line section for closing said emergency valve if the said pressure falls below a predetermined low value.

5. A boiler feed water system according to claim 1, in which the deaerator has water inlet nozzles the capacity of which nozzles is determined so as to exceed, by a small margin, the maximum flow quantity required between the condenser extraction pump and the boiler feed pump and in which the capacity of the pump in the discharge conduit of the deaerator is such as to be easily capable of extracting the whole of the water admitted through the nozzles and delivering such Water back to the feed line section.

6. A boiler feed water system according to claim 1, in which the deaerator is of the direct contact type, and further comprising means for supplying heating steam to the deaerator, a branch conduit from the deaerator adapted to afford a supply of saturated steam when required, and a valve for controlling said branch conduit.

7. A boiler feed water system for marine purposes according to claim 1, comprising an additional feed storage tank and a pump having its suction connected to said tank and its outlet connected to the boiler feed supply line section, the said pump being adapted to supply water to said line section at a pressure enabling the deaerator to be operated when the condensate extraction pump is out of action.

8. A boiler feed water system according to claim 1, in which the deaerator has water nozzles connected to separate inlet pipes and valves are provided for con trolling said pipes whereby certain of the nozzles may be cut out when required to reduce the quantity of water passing through the deaerator.

9. A boiler feed water system according to claim 1, comprising a heat exchange element comprising two separate paths for diiferent media, connections with the feed water inlet conduit to the deaerator for passing water through one of said paths, a conduit between one end of the other of said paths and the lower part of the deaerator, the other end of said other path being connected to an atmospheric vent whereby air and gases vented from the deaerator are cooled by heat exchange with the entering water.

References Cited in the file of this patent UNITED STATES PATENTS 928,665 Kelly July 20, 1909 1,972,356 Pfleiderer Sept. 4, 1934 1,983,422 Voorhees Dec. 4, 1934 2,339,369 Baker Jan. 18, 1944 2,371,443 Hillier Mar. 13, 1945 FOREIGN PATENTS 531,062 Great Britain Dec. 27, 1940 860,645 France Jan. 20, 1941 551,063 Great Britain Feb. 5, 1943 657,191 Great Britain Sept. 12, 1951 

